D A T A S H E E T
Locking Bit. This will permanently set the part to op-
dividual PPBs are programmable. It is the responsibil-
ity of the user to perform the preprogramming
operation. Otherwise, an already erased sector PPBs
has the potential of being over-erased. There is no
hardware mechanism to prevent sector PPBs
over-erasure.
erate only using Persistent Sector Protection. If the
customer decides to use the password method, they
must set the Password Mode Locking Bit. This will
permanently set the part to operate only using pass-
word sector protection.
It is important to remember that setting either the Per-
sistent Sector Protection Mode Locking Bit or the
Password Mode Locking Bit permanently selects the
protection mode. It is not possible to switch between
the two methods once a locking bit has been set. It is
important that one mode is explicitly selected
when the device is first programmed, rather than
relying on the default mode alone. This is so that it
is not possible for a system program or virus to later
set the Password Mode Locking Bit, which would
cause an unexpected shift from the default Persistent
Sector Protection Mode into the Password Protection
Mode.
Persistent Protection Bit Lock (PPB Lock)
A global volatile bit. When set to “1”, the PPBs cannot
be changed. When cleared (“0”), the PPBs are
changeable. There is only one PPB Lock bit per de-
vice. The PPB Lock is cleared after power-up or hard-
ware reset. There is no command sequence to unlock
the PPB Lock.
Dynamic Protection Bit (DYB)
A volatile protection bit is assigned for each sector.
After power-up or hardware reset, the contents of all
DYBs is “0”. Each DYB is individually modifiable
through the DYB Write Command.
The device is shipped with all sectors unprotected.
AMD offers the option of programming and protecting
sectors at the factory prior to shipping the device
through AMD’s ExpressFlash™ Service. Contact an
AMD representative for details.
When the parts are first shipped, the PPBs are
cleared. The DYBs and PPB Lock are defaulted to
power up in the cleared state – meaning the PPBs are
changeable.
When the device is first powered on the DYBs power
up cleared (sectors not protected). The Protection
State for each sector is determined by the logical OR
of the PPB and the DYB related to that sector. For the
sectors that have the PPBs cleared, the DYBs control
whether or not the sector is protected or unprotected.
By issuing the DYB Write command sequences, the
DYBs will be set or cleared, thus placing each sector in
the protected or unprotected state. These are the
so-called Dynamic Locked or Unlocked states. They
are called dynamic states because it is very easy to
switch back and forth between the protected and un-
protected conditions. This allows software to easily
protect sectors against inadvertent changes yet does
not prevent the easy removal of protection when
changes are needed. The DYBs maybe set or cleared
as often as needed.
It is possible to determine whether a sector is pro-
tected or unprotected. See “Autoselect Command Se-
quence” section on page 36 for details.
Persistent Sector Protection
The Persistent Sector Protection method replaces the
old 12 V controlled protection method while at the
same time enhancing flexibility by providing three dif-
ferent sector protection states:
■ Persistently Locked—A sector is protected and
cannot be changed.
■ Dynamically Locked—The sector is protected and
can be changed by a simple command
■ Unlocked—The sector is unprotected and can be
changed by a simple command
In order to achieve these states, three types of “bits”
are going to be used:
The PPBs allow for a more static, and difficult to
change, level of protection. The PPBs retain their state
across power cycles because they are Non-Volatile.
Individual PPBs are set with a command but must all
be cleared as a group through a complex sequence of
program and erasing commands. The PPBs are also
limited to 100 erase cycles.
Persistent Protection Bit (PPB)
A single Persistent (non-volatile) Protection Bit is as-
signed to a maximum four sectors (“Am29BDS128H
Boot Sector/Sector Block Addresses for Protec-
tion/Unprotection” section on page 16). All 4 Kbyte
boot-block sectors have individual sector Persistent
Protection Bits (PPBs) for greater flexibility. Each PPB
is individually modifiable through the PPB Program
Command.
The PBB Lock bit adds an additional level of protec-
tion. Once all PPBs are programmed to the desired
settings, the PPB Lock may be set to “1”. Setting the
PPB Lock disables all program and erase commands
to the Non-Volatile PPBs. In effect, the PPB Lock Bit
locks the PPBs into their current state. The only way to
clear the PPB Lock is to go through a power cycle.
Note: If a PPB requires erasure, all of the sector PPBs
must first be preprogrammed prior to PPB erasing. All
PPBs erase in parallel, unlike programming where in-
18
Am29BDS128H/Am29BDS640H
27024B3 May 10, 2006
SPANSION [ SPANSION ]
